Propylthiouracil tablet is indicated:

• in patients with Graves’ disease with hyperthyroidism or toxic multinodular goiter who are intolerant of methimazole and for whom surgery or radioactive iodine therapy is not an appropriate treatment option
• to reduce symptoms of hyperthyroidism in preparation for thyroidectomy or radioactive iodine therapy in patients who are intolerant of methimazole

Propylthiouracil inhibits the synthesis of thyroid hormones and is effective in the treatment of hyperthyroidism. It does not inactivate preformed thyroxine (T4) or triiodothyronine (T3) already stored in the thyroid gland or circulating in the blood. It also does not interfere with exogenously administered thyroid hormones. In addition, Propylthiouracil inhibits peripheral conversion of T4 to T3, making it particularly useful in thyroid storm.

Propylthiouracil is administered orally. The total daily dosage is usually given in 3 equal doses at approximately 8-hour intervals.

Adults: The initial dose is 300 mg daily. In patients with severe hyperthyroidism, very large goiters, or both, the initial dose may be increased to 400 mg daily; an occasional patient will require 600 to 900 mg daily initially. The usual maintenance dose is 100 to 150 mg daily.

Pediatric Patients: Propylthiouracil is generally not recommended for use in pediatric patient except in rare instances in which other alternative therapies are not appropriate options. Studies evaluating appropriate dosing regimen have not been conducted in the pediatric population although general practice would suggest initiation of therapy in patients 6 years or older at a dosage of 50 mg daily with careful upward titration based on clinical response and evaluation of TSH and free T4 levels. Although cases of severe liver injury have been reported with doses as low as 50 mg/day, most cases were associated with doses of 300 mg/day and higher.

Geriatric Patients: Reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

With medicines: Oral anticoagulants (e.g., warfarin) – Propylthiouracil may increase anticoagulant effect by reducing vitamin K activity, increasing bleeding risk. PT/INR monitoring is required, especially before surgery.

Beta-adrenergic blockers – Clearance may increase in hyperthyroid patients; dose adjustment may be needed after achieving euthyroid state.

Digitalis glycosides – Serum levels may increase when thyroid function normalizes; dose reduction may be required. Theophylline – Clearance may decrease when euthyroid state is achieved; dose adjustment may be needed.

With food: No specific dietary restrictions are required.

Hypersensitivity to propylthiouracil or any of its components.

Common: rash, urticaria, itching, hair loss, skin pigmentation changes, edema, nausea, vomiting, abdominal discomfort, loss of taste, joint and muscle pain, headache, leukopenia, agranulocytosis, hepatitis, hepatic failure.

Rare: aplastic anemia, drug fever, lupus-like syndrome, severe liver reactions, bleeding disorders, nephritis, interstitial pneumonitis, vasculitis, polymyositis.

Propylthiouracil crosses the placenta and may cause fetal goiter and hypothyroidism. Use the lowest effective dose after weighing risks and benefits. It is excreted in small amounts in breast milk; infants should be monitored during breastfeeding.

Patients should report immediately if symptoms like sore throat, fever, mouth ulcers, or infection occur due to risk of agranulocytosis. CBC monitoring is required. Stop treatment if neutropenia develops.

It may cause bleeding due to hypoprothrombinemia; monitor prothrombin time, especially before surgery. Severe hepatic reactions may occur; liver function should be monitored. Use with caution in liver or kidney impairment.

Not routinely recommended in children unless methimazole is not tolerated and other treatments are unsuitable. Parents should be informed about the risk of liver failure.

Symptoms include nausea, vomiting, abdominal discomfort, fever, headache, joint pain, itching, edema, and pancytopenia. Agranulocytosis is the most serious toxicity. Treatment is supportive.

Thyroid drugs & hormones

Store in a cool (below 30°C), dry place, protected from light and out of reach of children.